Error: Request Security Violation at /oauth/token

Hi,

I am trying to authenticate via OAuth2 with authorization code flow.  I am able to successfully generate code but when I try to exchange with an access token, it returns 200 success with an HTML "Error: Request Security Violation at /oauth/token". However, it does not tell what part of it has the security vi. 

olation.

This is the token url to exchange 

https://secure.na3.adobesign.com/public/oauth/v2/token

and I am adding the below value as part of the request

code=<authorization code>

grant_type=authorization_code

client_id=<account client id>

client_secret=<account client secret>

redirect_uri=<redirect uri set in the account>

Can you help me move this forward?